An ultra-short period rocky super-Earth with a secondary eclipse and a Neptune-like companion around K2-141

Luca Malavolta, Andrew W. Mayo, Tom Louden, Vinesh M. Rajpaul, Aldo S. Bonomo, Lars A. Buchhave, Laura Kreidberg, Martti H. Kristiansen, Mercedes Lopez-Morales, Annelies Mortier, Andrew Vanderburg, Adrien Coffinet, David Ehrenreich, Christophe Lovis, Francois Bouchy, David Charbonneau, David R. Ciardi, Andrew Collier Cameron, Rosario Cosentino, Ian J. M. CrossfieldMario Damasso, Courtney D. Dressing, Xavier Dumusque, Mark E. Everett, Pedro Figueira, Aldo F. M. Fiorenzano, Erica J. Gonzales, Raphaëlle D. Haywood, Avet Harutyunyan, Lea Hirsch, Steve B. Howell, John Asher Johnson, David W. Latham, Eric Lopez, Michel Mayor, Giusi Micela, Emilio Molinari, Valerio Nascimbeni, Francesco Pepe, David F. Phillips, Giampaolo Piotto, Ken Rice, Dimitar Sasselov, Damien Ségransan, Alessandro Sozzetti, Stéphane Udry, Chris Watson

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Ultra-short period (USP) planets are a class of low mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in-situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of an USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b we thus inferred a radius of 1.51 ± 0.05 R and a mass of 5.08 ± 0.41 M, consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV dataset, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30 ± 0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ∼3000K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios.
Original languageEnglish
Article number107
JournalAstronomical Journal
Issue number3
Publication statusPublished - 9 Feb 2018


  • Planetary systems
  • Planets and satellites: composition
  • Planets and satellites: individual (K2-141b, K2-141c)
  • Planets and satellites: interiors
  • Stars: individual (K2-141)
  • Techniques: photometric
  • Techniques: radial velocities


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